This invention relates to a superconducting rotating electric machine having a rotor whose windings are formed from a high-temperature superconductor. More particularly, it relates to a superconducting rotating electric machine having a novel cooling mechanism for cooling the rotor windings.
Until recently, the rotor windings of superconducting rotating electric machines were made from conventional superconductors such as NbTi and Nb.sub.3 Sn which have a critical temperature of at most 20 K. Because of their extremely low critical temperature, these conventional superconductors must be cooled by liquid helium. In a conventional superconducting rotating electric machine, the rotor windings were kept constantly immersed in liquid helium which was introduced into the inside of the rotor from one of its ends. The liquid helium cooled the rotor windings by evaporating and absorbing heat from the rotor windings. The vaporized helium was then removed from the rotor via one of its ends.
The latent heat of vaporization of liquid helium is extremely small, so in order to efficiently cool superconducting rotor windings, the rotor must be very carefully insulated. Therefore, the portion of the rotor which houses the rotor windings is generally separated from other parts of the rotor by a high vacuum.
Because of the difficulty of supplying liquid helium to the inside of a rotor which is rotating at a high speed, the structure of conventional superconducting rotors is extremely complex. Not only is the piping for supplying the helium complex, but it is also necessary to provide a mechanism for absorbing thermal strains which develop within the rotor.
Furthermore, it is difficult to maintain a high vacuum within the rotor over a long period of a year or more, and therefore conventional rotating electric machines have problems with respect to reliability.